Extend LocalizedString type to allow empty string

[maxpatiiuk]

Would it be possible to make LocalizedString typescript type that is provided by this library consider an empty string to be localized?

Example implementation

That might look like the following:

// Currently:
export type LocalizedString = string & {
    readonly [localized]: unknown;
};
// Requested:
export type LocalizedString = 
  | ''
  | (string & {
    readonly [localized]: unknown;
  });

Benefits

Empty string is often used as a placeholder/default value for a place that will store localized string.

• Good example is React state:

  // Without this change we need a type assertion:
  const [userName, setUserName] = React.useState('' as LocalizedString);
  // With this change
  const [userName, setUserName] = React.useState<LocalizedString>('');

• Another use case:

  declare const stringOrUndefined: LocalizedStirng | undefined;
  declare const capitalize = (b: LocalizedString) => LocalizedString;   
  
  // Without this change we need a type assertion:
  capitalize(stringOrUndefined ?? ('' as LocalizedString));
  // With this change:
  capitalize(stringOrUndefined ?? '');

Workarounds

So far I created a declarations.d.ts file like this to overwrite the type exported by this library:

import type { localized } from 'typesafe-i18n/types/runtime/src/core';

declare module 'typesafe-i18n' {
  export type LocalizedString =
    | ''
    | (string & {
        readonly [localized]: unknown;
      });
}

Unfortunately, not every tool supports declarations file (ts-node requires extra options, typescript-eslint has some weirdnesses; my co-workers reported problems in vs code too - the above fix doesn't work for them, even though tsc is fine with it)

Drawbacks

There are cases where TypeScript may expand '' to mean string, thus negating the benefit of LocalizedString type.

[ivanhofer]

Hi @maxxxxxdlp, thanks for your suggestion, but I prefer not to do so.
Types should be as strict as possible, and you can opt out any time by using a cast (as LocalizedString) or a utility function that does the cast (const l = (value: string) => value as LocalizedString).
Also the workaround you already have mentioned is a good way to customize the behavior if you really want it in your projects. It is unfortunate but not typesafe-i18ns fault that the tooling does not support standard TypeScript features.

[maxpatiiuk]

No problem, thanks!